When issuing attack/transfer orders in games with no-split mode enabled, it is impossible to set the number of armies to attack or transfer. Instead, all available armies will always attack or transfer.
In other words, if you have a big stack of armies, it isn’t possible to split that stack into smaller stacks. They must stay together forever. This changes the game’s strategy quite a bit, since you need to be conscious of when you want to combine armies onto the same territory.